Process for the production of sodium bifluoride



y 8, 1952 E. A. WINTER 2,602,726

PROCESS FOR THE PRODUCTION OF SODIUM BIFLUORIDE Original Filed June 23, 1948 l5 I NO F H siF SOLUTION MIXER ABSORPT! 7 v1 TOM/E SIP, 1

" VV ET O9- NQHFZ SLURRY ,'"----"1 a-e'ZkhHF STILL 'g SOLUTION M L ;;T|:NAL

war ppidNa siF NQHFZ +lO F u fi 3 HIE? F '1 E I Snu. DRY M sai- L 16 l a aFTToNM.

- HF H2O DRYER. VAPOR new NQ SKF FURNAC INVENTOR Errzasi' A. I Vinier ATTORNEYS Patented July 8, 19 52 2,502,726 I p r PROCESS For: THE PRODUCTION or SODIUM BIFLUORIDE Ernest A. Winter, College Park Ga., assignor to Tennessee poration of New York {.Qriginal application ,7 June 23, 1948, Serial No.

34,716. Divided and this application September 24, 1951, SerialNo. 248,031

This invention relates to the production of essentiallysilicon-free fluorine compounds and more particularly to the production of sodium bifluoride from hydrofluosilicic acid (HzSiFs).

" This application is a division of copending application Serial No. i 34,? 16,

V V filed June 23, 1 948, IiOW. Patent NO. 2,588,786. 7'

Corporation, New York, N. Y., a cor-' Edition, volume 5, page 27 8 et seq., describes The process of the present invention may em ploy hydrofiuosilicic acid as the starting compound andlemploys NazsiFe, NaF and H at fierent stages in the-process to produce HF; sodium bifluoride (NaHFz);' sodium fluosilicate -'(Na2SiFs) and sodium fluoride T (NaF) Heretofore sodium bifiuoride has been prepared from HF made from'fiuorspar and sulphuric acid.

This fluorspar must be of high grade and substantially free of impurities to produce the desired end products. Deposits of this fiuorspar are now being depleted and the process of thepresent inventionmakes use of a'hitherto'waste product, HzSiFs, to produce sodium bifluoride on a. competitive'basis with known commercial processes. HzSiFe is a by-productand is recovered from waste gases generated insuperphosphate manufacture. v 1

It is accordingly an object of the present invention to produce sodium bifluoride from hydrofluosilicic acid. l v Another object of the present invention is to acid made from hydrofiuosilicic acid.

Another object of the present inventionlis to produce sodium bifluoride from hydrofluosilicic acid without employing expensive raw materials.

Another object of the present invention is to produce sodium bifluoride from hydrofluosilicic acid by processes in which by-products maybe recycled in such processes to reduce the cost of the raw materials employed therein.

Other and further objects of the present invention will appear from the following description.

In the accompanying drawing a flow sheet is provided of an illustrative embodiment of the process of the present invention.

It is well known to the art that hydrofluoric acid and water form a constant boiling mixture which contains approximately 38% HF and 62% H20. If such a solution has less than 38% HF it cannot be fractionated to give a higher strength than 38%. If such a solution has approximately 80% HF it can be fractionated to yield substantially 100% HF gas and a liquid residue of 40-50% HF. In the following description of my invention when I refer to dilute HF solutions I mean soluproduce sodiumbifiuoride from dilute hydrofluoric present methods for producing HF which have heretofore been based primarily upon the reaction of relatively pure fluorspar and sulphuric acid. This HF can be reacted with, e. g., NaOH to form NaHFz. Since, as heretofore noted, deposits of high grade fiuorspar are being depleted it is now necessary that other sources of basic material be foundfor the production of sodium bifluoride; and hydrofluosilicic acid is a by-product, and in many cases a waste material, of the acidulation of phosphate rock' in the fertilizer industry. Hydrofluosilieic acid has heretofore been used to produce fluosilicates employing the reactions:

The patent to Buchner No. 1,664,348 discloses following reaction:

I have found that the dilute HF Saunas: of formula (2) may be treated by the addition of 'NaF to the solution to precipitate NaHFz, a relatively insoluble compound, lowing formula:

The NaHFz may then be filtered off and dried.

The several formulae discussed above may be utilized in an economic commercialprocess as disclosed in the flow diagram of the drawing. In this diagram an 18% HzSlFs solution, which is obtained as a by-product from the manufacture of phosphate fertilizer, is taken to an absorption tower I where it is treated with a strong SiF4 gas which may be refluxed from a later stage in the process as will more fully appear hereinafter. HzSiFe is formed in absorber I having approximately 30% concentration with the precipitation of silica or silicic acid according to the formula:

(4) 3siF4+2H2o 2H2siF6+sio2i The SiOz is filtered OE and the HzSiFs solution is according tothe folremoved to mixer 2 where at least an equivalent The following reaction takes places in mixer 2:

() 2H2SiFe 4NaF- 2NazSiFst +4HF It should be noted that if too much NaF is added the otherwise free HF will be precipitated as NaHFz. The products of reaction (6) are then taken to filter 3 where the precipitated NazSiFc is separated from the 1-H solution. The HF solution is taken to mixer l. The wet NazSiFs is taken from filter 3 to dryer 4 where it is dried and the HF gas and water vapor produced therein are led from dryer 4 to mixer l. The dried NazSiFs is removed to furnace 5 where it is calcined to produce SiF4. This SiF4 is refluxed through a suitable cooler 6 to absorption tower l and the NaF which is produced is refluxed to mixer 2. The reaction taking place in furnace 5 is:

(6) 2Naz-SiFc+heat- 4NaF+2SiFtT The HF solution taken from filter 3 and dryer 4 may be passed through suitable stills l6 before admission to mixer 1 to fractionate such solutions mac-35 HF. Stills [6 are shown as optional in the drawing. Where fuel costs are low it is desirable to so fractionate these HF solutions because-the resulting yield of NaHFz will. be

higher.

The HF solutions from filter 3 and dryer 4, fractionated or not as the case may be, are mixed in mixer I with NaF. The reaction taking place in mixer I is:

,in dry state constitutes a commercial article. H ,In the process described above with reference to the flow diagram of the drawing the concentrations there employed maybe varied and if a stronger HzsiEs solution is available then the yield will be higher. Room temperatures are employed in the various stages of the process except, in the dryers, furnaces, calciners, etc. Recycling of NaF and SiF4 reduces the cost of the operation but it is obvious that 'NaF and/or NazSiFc must be added to the system to make up for losses.

By the present invention I have provided a novel process for the production of sodium bifluoride from hydrofluosilicic ,acid; in,w hich sodium bifiuoride is producediron'i diluteYI-IF; and in which this compound is produced from hydrofiuosilicic acid without the use of expensive raw materials. I Changes to or modifications of the above described illustrative embodiments of my process may now be suggested to those skilled in the art without departingv from my inventive concept. The various temperatures and concentrations employed are illustrative and may be varied. Heat generated in the calciners and furnaces may be employed 'to preheat and to dry at various stages'of the processes. Reference should therefore be had to the appended claim to determine the scope of this invention.

What is claimed is: l

In a process for obtaining sodium bifluoride from hydrofiuosilicic acid the steps of treating a solution of hydrofiuosilicic acid with sodiumfluoride to form hydrofluoric acid-in solution and precipitate sodium 'fluosilicate, separatingthe sodium fluosilicate from the hydrofluoric acid solution, heat treating the sodium fluosilicate to obtain sodium fluoride, cycling the sodium fluoride back to the step of mixing the solution of hydrofluosilicic acid with sodium-fluoride and treating the hydrofluoric acid solution ,with sodium fluoride lac-precipitate sodiumibifluoride.

I ERNEs'rA.'vvnv'rtrgn.

REFERENCES CITED The following references are of record in the file of this patent; I

UNITED STATES PATENTS Number Name 7 g p Date 1,664,348 Buchner W Nov. 27,1928

OTHER REFERENCES Long'mans, Green & Col, N. 

